/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMesh3.h
Rewrite the triangle to reference the new tuple of vertices.
virtual [EMeshResult](API\Runtime\GeometryCore\UE__Geometry__EMeshResult) SetTriangle ( int TriangleID, const [FIndex3i](API\Runtime\GeometryCore\FIndex3i) & NewVertices, bool bRemoveIsolatedVertices )